Polarized Light in Animal Vision and Ecology
What is polarized light?
Light coming from the sun is unpolarized, meaning the direction of the electromagnetic vibration of the photons are random. If that light interacts with the atmosphere, water bodies, or other objects, the photons in a sample of light can all start to vibrate in th same direction (e.g. horizontally). One of the most common sources of polarized light on earth is water. Light that reflects from its surface is 100% polarized. Light that enters the water, and is later reflected back outward may be unpolarized and mixes with the reflected light such that natural water bodies reflect somewhere between 35-80% of reflected light, depending on their depth, smoothness, turbidity and substrate color.
Every terrestrial animal ever tested has been revealed to have the ability to see polarized light and use it to locate water (including humans). However, polarized light can provide all kinds of other information useful to animals such as the direction of the sun, the quality of a mate, the direction of prey, and much more. Much is unknown, especailly in the terrestrial environment as more research has focused on the aquatic and marine environments.
Polarized light use by terrestrial animals
I have focused my research on how terrestrial animals use polarized light. Much of my research for the last 10 years has focused on aquatic insects. I've examined the details of the polarization cues they use to guide their water-seeking behavior, and how their behavior is tuned to use these cues adaptively in the wild and maladaptively in the presence of artifical sources of polarized light (i.e. polarized light pollution). I've done much of this work within the context of understanding evolutionary traps, but my new researh (see below) is more focused on the evolutionary bases and functional value of polarized light in bird and butterfly plumage. This research is just beginning.
Do you study polarized light?
Scientists who study of polarized light and how it relates to animal vision and behavior are trained in all types of fields and are typically interdisciplinary in their approach to science and conservation. If you are one of these people, I'd love to hear from you, especially if you are interested in contributing to a new, image-based project, called "The Polarized World" that I'll be creating (see Home page, bottom).